Abstract:
Organic aerogel is a nano-porous solid material with network structure formed by crosslinking of colloidal particles or polymer. In these pores were filled with gas dispersion medium. Because of their unique nanostructure, all types of aerogel show a very low thermal diffusivity, refractive index, speed of sound and resistivity. Therefore, these kind of material shows a promising future in fields of preparation of heat-or sound-insulating materials, environment preservation, catalyst, absorbents and capacitor with high performance. Wood is a nature porous material with pores of different sizes. To modify wood with aerogel to get wood/aerogel composite will make use of the organic or inorganic nanoparticles in aerogel and combine the advantages of both wood and aerogel together. It is one of the modification methods of wood. To put organic aerogel embedded evenly in intercellular space, specifically, space between cell walls and lumens, and study the modification method, procedure and mechanism will resolve some practical problems confronted in the application of aerogel. And at the same time, the modification may offer wood some new functions.In this thesis, organic aerogel was fed into the pores of wood by sol-gel method and vacuum impregnation. The process was optimized with response surface approach. The wood/aerogel composite was dried by supercritical fluids to let the polymer left in the wood keep the net structure with nanometer size. The preparation method and the microstructure, crystalline structure, chemical structure and physical performance were analised in this work. Some conclusions could be drawn:(1) The factors to prepare resorcinol-formaldehyde (RF), such as gel temperature, addition amount of catalyst and reactant concentration, were optimized by response surface approach. A model with good fitness to predict the gel time of RF was gotten:R1=23.22-0.58*A+0.18*B-0.64*C-2.35×10-3*A*B-1.80×10-4*A*C+1.73×10-3*B*C+4.38×10-3*A2-6.07×10-5*B2+1.80×10-2*C2. The optimized vacuum impregnation procedures were as below:the samples was treated with former pressure0.03MPa for30min, with impregnation pressure0.8MPa forl.5h and with latter pressure0.09MPa for10min. The results of SEM, XRD, FTIR, TG indicated that wood/RF-based aerogel composite had evenly filling network structure. RF aerogel didn’t change the crystallization structure of wood by its own. There were both chemical bonding and physical filling existed between aerogel and wood. The resulted wood/RF aerogel had good dimension stability, mechanical performance and ageing resistance.(2) The factors to prepare melamine-formaldehyde (MF), namely, gel temperature, addition amount of catalyst and reactant concentration, were optimized by response surface approach. A model with good fitness to predict the gel time of MF was gotten:R1=45.60- 29.75*X1+2.50*X2-13.75*C-2.00*A*B+5.50*A*C+1.50*B*C-0.30*A2+0.20*B2-4.30*C2. The optimized procedure for preparation of MF were as below:reactant concentration,8%; pH,1.5; gel temperature,95℃. The resulted MF aerogel had network structure and uniform component organic particles. Wood/MF aerogel composite could be gotten by vacuum impregnation and drying with supercritical fluids. The result of SEM showed that MF aerogel in the wood had network structure. The result of XRD indicated that the filling of MF aerogel in the wood would not destroy the crystallization structure of wood. Because of the chemical bonding between MF aerogel and wood, which was proved by FT-IR, the resulted composite had better heat resistance. The composite had better dimension stability and mechanical performance.(3) The optimized procedure for preparation of RMF was molar ratio M/R4, reactant concentration10%and gel temperature95℃. The wood/RMF composite prepared by the way of vacuum impregnation had similar color, crystallization and chemical properties as those of wood without RMF. RMF could got gelatinization in a short time, which would be good to the preparation of wood/RMF composite. Because of the network structure and low thermal conductivity of RMF aerogel, the wood/RMF aerogel composite showed good heat and noise insulation.(4) The inorganic/organic aerogel could be gotten by simply blending TiO2or SiO2inorganic sol with MF organic sol. The results of SEM, XRD, FT-IR and TG indicated that inorganic particles were in-situ polymerized in the network of MF aerogel. Wood/aerogel composite were prepared with MF/inorganic particles aerogel by vacuum impregnation method. The results of SEM, XRD, FT-IR and TG showed that TiO2dispersed in the wood, while interpenetrating polymer network with SiO2could be seen. When modified with octadecyltrichlorosilane, wood with aerogel mixed with inorganic particles showed super hydrophobic performance. The accelerated ageing test indicated that the wood/aerogel composite with inorganic particles had a good UV resistance.(5)To modify wood with organic aerogel or organic aerogel with inorganic nano-particles provide a new idea and method to prepare wood with new functions. The resulted material will further extend the application field of wood.